The present disclosure relates, in various exemplary embodiments, to display devices comprising a metal-organic mixed layer as part of an anode configuration. In particular, the present disclosure relates to display devices comprising a metal-organic mixed layer as part of an anode and operatively combined with an electron-accepting material. While the anode configurations are described with particular reference to organic light emitting devices (OLEDs), it will be appreciated that the anodes are amendable to other similar applications and display devices.
Organic light emitting devices (OLEDs) represent a promising technology for display applications. A typical organic light emitting device includes a first electrode; a luminescent region comprising one or more electroluminescent organic material(s); and a second electrode; wherein one of the first electrode and the second electrode functions as a hole-injecting anode, and the other electrode functions as an electron-injecting cathode; and wherein one of the first electrode and the second electrode is a front electrode, and the other electrode is a back electrode. The front electrode is transparent (or at least partially transparent) while the back electrode is usually highly reflective to light. When a voltage is applied across the first and second electrodes, light is emitted from the luminescent region and through the transparent front electrode. When viewed under high ambient illumination, the reflective back electrode reflects a substantial amount of the ambient illumination to the observer, which results in higher ratios of reflected illumination as compared to the device's own emission resulting in “washout” of the displayed image.
In order to improve the contrast of electroluminescent displays in general, light-absorbing layers as described, for example, in U.S. Pat. No. 4,287,449, or optical interference members as described, for example, in U.S. Pat. No. 5,049,780, have been used to reduce the ambient illumination reflection.
Other recent developments in reducing the reflection of ambient light in display devices have been directed to metal-organic mixed layers such as described in, for example, U.S. patent application Ser. No. 10/117,812, now U.S. Pat. No. 6,841,932, and U.S. patent application Ser. No. 10/401,238, which is published as U.S. Pat. Publication No. 2003/0234609. Other methods to reduce light reflection are addressed in U.S. Pat. No. 6,750,609. These applications and patents are incorporated herein by reference in their entirety.
Anodes in display devices such as OLEDs are typically formed from materials such as ITO. The use of ITO has disadvantages, however, in that ITO cannot be readily fabricated by thermal vapor deposition techniques commonly used to make or form the other components of the OLED. An ITO anode usually requires more aggressive fabrication techniques such as sputtering and is therefore fabricated separately from the rest of the OLED to avoid damaging the relatively fragile organic stack and components of the adjacent layers. This results in an increase in both the time and cost required to manufacture or form a OLED structure. There is thus a need to provide a material or configuration for an anode that allows the anode to be formed using deposition techniques that are used to form the other layers of the OLED.
Additionally, non-reflective anodes (black anodes) are important for top-emitting devices in which the driving electronic circuitry is located on the anode side instead of the cathode side of the display device as in the case of regular bottom-emitting OLEDs. While metal-organic mixed layers as described in the afore mentioned patents and applications, have been demonstrated as suitable for a cathode, material incompatibility issues have posed problems for their use as non-reflective or black anodes.
Therefore, there is a need for new anode materials and/or configurations. A need exists for anode configurations and materials that are amenable to less aggressive deposition techniques such as, for example, thermal deposition. There is also a need for an anode configuration that allows for tuning the transparency or opacity of the anode to be controlled such that the anode and/or OLED may be made substantially reflective, substantially light absorbing (e.g. black), or substantially transmissive (e.g. transparent or semitransparent), as desired.